Directional slot antenna



J y 29, 1952 H. J. RIBLET DIRECTIONAL SLOT ANTENNA Filed April 11, 1946 B i L y {NVENTOR HENRY J. RIBLET ATTORNEY Patented July 29, 1952 STATES PATENT OFFICE Y $605,411 7 v I DI ECTIONAL SLOTANTENNA I v Henry J Riblet, Erie, Pa., assignor, by mesne as sigmn'ents, to the United States of America as represented by the Secretary of the Navy Application April 11, 1946, Serial Nb. 661,206

This invention relates to antenna systems and more particularly to such systems using lumped reactances to suppress radiation in a given direction;

To reduce the resistance to air flow of the outer surface of an aircraft it has been desirable to replace rod antennas with slotted antennas. The slotted antenna consists of a narrow slot cut in the outer metallic skin of an aircraft. The slot is fed in such a manner (as will be made clear below) that the distribution of energy along the slot approximates that of a half wave antenna. Thus conditions for efiicient radiation are satisfied, and effectively the slot becomes a dipole. There are normally radiations in two directions; both directions'being perpendicular to the surface of the aircraft. The radiation out from the surface of the plane is desirable but the radiation into the interior of the plane is unde-' sirable in that it diverts one half of the total radiated energy. It is also undesirable to have uncontrolled radiation in the interior of the aircraft. Heretofore radiation into the interior of the aircraft has been suppressed by. enclosingthe inner surface of the skin immediately adjacent to the radiating slot in a metal box, thus making radiation into the interior an impossibility. There were two outstanding difficulties encountered in the practical application of this method. The first was that in an aircraft containing a multiplicity of slotted antennas, the space and weight contributed bythe metal boxes was appreciable. The second and more serious difficulty lay in the nature of the metal boxitself. The inner surface of the box acted as a cavity. Unless the resonant frequency of the cavity was the same as the radiating frequency of the slot, the cavity would absorb energy from the radiating slot and much of the advantage gained from suppressing radiation into the interior would be lost. It was possible with careful design to prepare a metal box whose resonant frequency was the same as that of the radiating slot; but in the case of an antenna called upon to perform on a number of different frequencies, it was then necessary to have a different box for each frequency.

The general object of the present invention is to suppress effectively the radiation on one side of a radiating slot.

Another object of the presentinvention is to provide a backing on one side of the slotto suppress radiation on that side of the slot.

Still another object is to provide a lumped reactance to be used as a backing for the slot.

A further object is to provide atuned or untuned means as the required lumped reactance.

A still further object is to provide a metal loop 8 Claims. (Cl. 250-33) 2 or multiplicity of metal loops to provide the lumped reactance. These and other objects will become apparen from the following specificationwhen taken in connection with the accompanying drawing in which:

Fig. 1 is a perspective view of one form of the invention; e

Fig.2 a top axial sectional view of the rep resentation in Fig. 1 taken along the line IIII ofFig.l; v Fig. 3 is a front sectional view of the representation in Fig. 1 taken along the line III- 111 of Fig. 1.

The present invention uses a lumped reactance to suppress undesired radiation. If a lumped reactance with proper constants is placed behind the slot. then the slotted antenna will radiate back into a circuit at its resonant frequency and the same set of conditions will exist'as though there were a metal box backing the slotted antenna. The lumped reactance may take many forms and, dependent upon the use of the an tenna. may be either fixed or variable. For the purposeof illustration only, a fixed reactance is shown. I

Referring now to Fig. 1, a metallic sheet l0, which may'the outer covering of an aircraft,'has a slot I I out therein. A coaxial linelZ, comprising'a center conductor l3 and an outer conductor I4, is split into sections l5 and It at one end, and is used to feed slot ll. Metallic loops l1 and [8 are fixedly attached to the inside of sheet In in such a manner that the center of each of loops i1 and I8 is directly over slot ll. Metallic loops I! and [8 contain capacitance and inductance and thus act as lumped reactances. Referring to Fig. 2 there is shown the method of energizing slot l l. Section [5 of outer'conductor I4 is connected directly to wall In onone side of slot H. Inner conductor l3 is connected to wall ill on the opposite side of slot H. A potential difference equal to that between the inner conductor I3 and outer conductor [4 is thus set up across the opposite walls of slot ll.

Referring to Fig. 3, the structure of slot II is shown in greater detail. Signal voltage is applied across the center of slot II at point (a), and therefore the greatest difference of potential appears at the center. There is no potential difference across the slot at points (22) and (c). It is thus seen that the distribution of voltage along slot I I will 'resernble'that of a half wave antenna with the maximum potential at the cen-: ter and-a minimum potential at the ends. I In operation center conductor i3 and outer conductor l5 (Fig. 2) supply energy to point (a) invention has been disclosed and described it isto be understood that various changes and modi fications may be made therein without departing from the scope thereof as set forth in the an:

pended claims.

What is claimed is:

1. An antenna system comprising a conductive sheet having a slot formed therein, means for energizing said slot with radio frequency. energy whereby energy may be radiated from said slot oneither side of said; sheet, and means incln ding; a plurality of conductive loopsconneeted tosaid; conductive sh et n. a trans erse b d in r l tionsh p. to. said slot. said 1 rs bein dis os d on one side of said: conductive sheet whereby; radiation from said slot on said last mentienedside of said sheet is suppressed.

2. Antenna system comprising a conductive sheet having a slot formed therein, meansfor energizin aid slot with-radio frequency energy whereby energy may be radiated from said'slot. on either side of said sheet, and means including afirst. and-second conductive loop connected to said conductive sheet at one side thereof, said f rst loop being disposed across and at right ang es. to aid ot. at a p i t i er ia the center of, said slotand a. first end of said slot, said SB Q 1 being 15.1 58. GrOss and at right. angles to sa d sl a a m n med a e saidcenterofsaid slot anda second end of said slot. whe eby radiati n ienercy f o sa d slo on-the-side of said sheet including said loops is uppress d- 3. An antenna system comprising a conductive sheet having a slot formed therein, means for energizing said slot with radio frequency energy comprising a coaxial line having the outer conductor thereof connected to'said sheet at one side of said slot and the inner conductor thereof connected to said sheet at the otherside of said slot, first and second U shaped conductiv members, said first conductive member being disposed a righ angles o said slo at a osi io i t r m diat a i s end f. aid o nd, he o nt ef connect o of sa d transmi s n n the e d e said -shap d m b be ng nne e to aid heet on opp s s s 0i aid lot. aid second u-shaped member being similarly disposed and conn cted at a poi t inte media e sec n e of said slot and the point of connection ofsaid transmission line.

4. Anantenna system comprising a conductive sheet having a slot formed therein, means f r ne z n d slot ith radio requents! en r y compris n a oax a l n h ing t outer conductor thereof connected to said sheet at one side of said slot and the inner conductor thereof connected to said sheet at the other side of said slot, f rst and second U-shaped conductive meme member being similarly disposed and connected at a point intermediate a second end of said slot and the point of connection of said coaxial line.

5. An antenna system comprising a conductive sheet having a slot formed therein, means for energizing said slot with radio frequency energy comprising a two-conductor transmission line having the one conductor thereof connected to said sheet at one side of said slot and the other conductor thereof connected to said sheet at the other side of said slot, first and second U-shaped conductive. members, said first conductive memberbeing disposed at right angles to said slot at a position intermediate a first end of said slot and the point of connection of said transmission line, the ends of said U-shaped member being conductively connected to said sheet on opposite sides of said slot, said second U-shaped member bein sim arl i ed n nne t e point intermediate a second end of said slot and the point of connection of said transmission line.

6. An antenna system comprising a conduc-- tive sheet having aslot formed therein, a transmission line coupled'tov said slot midway between the ends thereof; and means including a firstand ee ondconductive loop connected to said conduc tive sheet at one side thereof, said first loop be.. ing disposed across saidslot and at right angles thereto at a point intermediate said transmission line and a first end of said slot, said second loop, bein disposed across said slot and at right. angles thereto at a point intermediate said trans? mission line and a second end of said slot where.- by radiation of energy fro n said slot on the side a, of said sheet including said loops is suppressed.

n n n stem com ri i e ee due: tive sheet having a slot formed therein, means. for energizing said slot with radio frequency energy, said means being such that energy may be radiated from said slot on either side of said sheet,- and a plurality of spaced conductive loops disposed across said slot on one side of said sheet, said loops being conductively connected to said sheet whereby radiation from said slot on the side of said sheet including said loops is suppressed.

8. An antenna system comprising a concisetive sheet having a slot. formed therein, means fo en r i in sa t th. radio u ncy. energy. substantially at the midpoint thereof, andv a plurality of conductive loops conductively connected across said slot on one side of said shee and s c rom a h other and frerh said.

' ener iz means w e eby r iat n from. aid

hers, said first conductive member being disposed at right angles to said slot and perpendicular to said sheet at a position intermediate a first end of said slot and the point of connection of. said coaxial line, the ends of said U- -shaped member being conductively connected to said sheet on oppos e si e of said slot. said se on =s a e antenna system on the side of said sheet includ ns sa le s s ppres ed- HENRY' J. RIBLET.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED srarns PATENTS OTHER REFERENCES Serial No. 353,755, publication of Dallenbach ci- .P- e publis d Ma .2 9 s- 

